One-Pot Synthesis of Oxidation-Sensitive Supramolecular Gels and Vesicles

A.D.-C. and G.B. acknowledge the Royal Society (Newton International Fellowship scheme 2017.NF171487) and EU H2020 MSCA-IF-792957 SPeNTa-Brain. The authors thank the ERC for the consolidator award (CheSSTaG 769798), EPSRC Established Career Fellowship (EP/N026322/1) and Jeol and DENS Solutions for sponsoring LPR salary, and part of C.D.P. and G.M. studentships. L.R.-A. thanks the UK's ESPRC for funding her salary (Grant EP/N026322/1) and acknowledges support by the Spanish State Research Agency (Spanish Ministry of Science and Innovation) through Juan de la Cierva Incorporacion Fellowship (IJC2018-037951-I). The authors thank Prof. Modesto T. Lopez-Lopez (University of Granada, Spain) for helpful discussions about gel rheology, Dr. Inmaculada Conejos (CIPF, Valencia, Spain) for her help with the CD, and Gabriel Ing (University College London, UK) for his support with transmission electron microscopy.Polypeptide-based nanoparticles offer unique advantages from a nanomedicine perspective such as biocompatibility, biodegradability, and stimuli-responsive properties to (patho)physiological conditions. Conventionally, self-assembled polypeptide nanostructures are prepared by first synthesizing their constituent amphiphilic polypeptides followed by postpolymerization selfassembly. Herein, we describe the one-pot synthesis of oxidation-sensitive supramolecular micelles and vesicles. This was achieved by polymerization-induced self-assembly (PISA) of the N-carboxyanhydride (NCA) precursor of methionine using poly(ethylene oxide) as a stabilizing and hydrophilic block in dimethyl sulfoxide (DMSO). By adjusting the hydrophobic block length and concentration, we obtained a range of morphologies from spherical to wormlike micelles, to vesicles. Remarkably, the secondary structure of polypeptides greatly influenced the final morphology of the assemblies. Surprisingly, wormlike micellar morphologies were obtained for a wide range of methionine block lengths and solid contents, with spherical micelles restricted to very short hydrophobic lengths. Wormlike micelles further assembled into oxidation-sensitive, self-standing gels in the reaction pot. Both vesicles and wormlike micelles obtained using this method demonstrated to degrade under controlled oxidant conditions, which would expand their biomedical applications such as in sustained drug release or as cellular scaffolds in tissue engineering.Royal Society of London European Commission 2017-NF171487EU H2020 MSCA-IF-792957 European Research Council (ERC) European Commission CheSSTaG 769798UK Research & Innovation (UKRI)Engineering & Physical Sciences Research Council (EPSRC) EP/N026322/1Jeol and DENS SolutionsUK's ESPRC EP/N026322/1Spanish State Research Agency (Spanish Ministry of Science and Innovation) IJC2018-037951-

Phagocytosis-inspired behaviour in synthetic protocell communities of compartmentalized colloidal objects

The spontaneous assembly of micro-compartmentalized colloidal objects capable of controlled interactions offers a step towards rudimentary forms of collective behaviour in communities of artificial cell-like entities (synthetic protocells). Here we report a primitive form of artificial phagocytosis in a binary community of synthetic protocells in which multiple silica colloidosomes are selectively ingested by self-propelled magnetic Pickering emulsion (MPE) droplets comprising particle-free fatty acid-stabilized apertures. Engulfment of the colloidosomes enables selective delivery and release of water-soluble payloads, and can be coupled to enzyme activity within the MPE droplets. Our results highlight opportunities for the development of new materials based on consortia of colloidal objects, and provide a novel microscale engineering approach to inducing higher-order behaviour in mixed populations of synthetic protocells

How nonmagnetic particles intensify rotational diffusion in magnetorheological fluids

In this work we propose a mechanism to explain the enhancement of the magnetic field-induced yield stress when non-magnetic particles are added to magnetic particulate suspensions –i.e., bi-component suspensions. Our main hypothesis is that the non-magnetic particles collide with the field-induced magnetic aggregates under shear flow. Consequently, supplementary fluctuations of the orientations of the magnetic aggregates occur, resulting in an effective rotary diffusion process, which increases the dynamic yield stress of the suspension. Furthermore, the collision rate and the rotary diffusivity of the aggregates should increase with the concentration of non-magnetic particles. Rheological measurements in plate-plate and cylindrical Couette geometries confirm the increase of the yield stress with the volume fraction of non-magnetic particles. In addition, such an effect appears to be more important in Couette geometry, for which orientation fluctuations of the magnetic aggregates play a more significant role. Finally, a theoretical model based on this rotary diffusion mechanism is developed, providing with a quantitative explanation to the experimentally-observed trends.This work was supported by Project No. FIS2013-41821-R (Ministerio de Economía y Competitividad, Spain) and the project “Factories of the Future” (Grant No. 260073, DynExpert FP7). In addition, L.R.-A. acknowledges financial support from Secretaría de Estado de Educacion, Formación´ Profesional y Universidades (MECD, Spain) through its FPU and Estancias Breves programs

La satisfacción familiar de un grupo de jóvenes de 18 a 25 años del municipio de Madrid Cundinamarca

La presente investigación gira en torno a la familia y busca comprender el nivel de satisfacción que tiene un grupo de jóvenes del municipio de Madrid Cundinamarca respecto a su sistema familiar, a partir de sus percepciones y juicios de valor que tenga el joven de su familia

Inverse magnetorheological fluids

We report a new kind of field-responsive fluids consisting of suspensions of diamagnetic (DM) and ferromagnetic (FM) microparticles in ferrofluids. We designate them as inverse magnetorheological (IMR) fluids for analogy with inverse ferrofluids (IFFs). Observations on the particle self-assembly in IMR fluids upon magnetic field application showed that DM and FM microparticles were assembled into alternating chains oriented along the field direction. We explain such assembly on the basis of the dipolar interaction energy between particles. We also present results on the rheological properties of IMR fluids and, for comparison, of IFFs and bidispersed magnetorheological (MR) fluids. Interestingly, we found that upon magnetic field, the rheological properties of IMR fluids were enhanced with respect to bidispersed MR fluids with the same FM particle concentration, by an amount greater than the sum of the isolated contribution of DM particles. Furthermore, the field-induced yield stress was moderately increased when up to 30 % of the total FM particle content was replaced with DM particles. Beyond this point, the dependence of the yield stress on the DM content was non-monotonic, as expected for FM concentrations decreasing to zero. We explain these synergistic results by two separate phenomena: the formation of exclusion areas for FM particles due to the perturbation of the magnetic field by DM particles, and the dipole-dipole interaction between DM and FM particles, which enhances the field-induced structures. Based on this second phenomenon, we present a theoretical model for the yield stress that semi-quantitatively predicts the experimental results.Projects 12-01-00132, 13-02-91052, 13-01-96047, 14-08-00283 (Russian Fund of Fundamental Investigations), 2.1267.2011 (Ministry of Education of Russian Federation), the Act 211 (Government of the Russian Federation № 02.A03.21.0006). The University of Granada (Acción Integrada con Rusia; Plan Propio 2011). L. Rodríguez-Arco acknowledges financial support by Secretaría de Estado de Educación, Formación Profesional y Universidades (MECD, Spain) through its FPU program

Stability behaviour of composite magnetorheological fluids by an induction method

Este artículo puede consultarse en la siguiente dirección de la editorial: http://jim.sagepub.com/content/early/2015/03/26/1045389X15577656.full.pdf+htmlIn this work we study the stability behaviour of composite magnetorheological (MR) fluids consisting of magnetic (iron) and non-magnetic (poly (methylmethacrylate), PMMA) particles dispersed in mineral oil. Because of the opacity of the suspensions, optical methods traditionally employed for evaluation of the gravitational settling in colloidal suspensions are not suitable for sedimentation follow-up in this case. For this reason, we use an alternative method based on the evaluation of the resonant frequency of the inductance of a thin coil surrounding the sample The movement of the coil along the height of the container at specified steps and time intervals allows obtaining information about the local volume fraction of particles inside the tube. The obtained successive profiles for the multi-component suspensions show a decrease of the iron particle settling and of the initial rate of settling as the PMMA volume fraction is increased. Finally, the increase of the PMMA concentration gives rise to an improvement of the rheological properties upon magnetic field application for a given concentration of iron. Both a strongrheological response and a good colloidal stability are essential for practical applications.Proyectos PE2012-FQM694 (Junta de Andalucía, Spain)y FIS2013-47666-C3-1-R (Ministerio de Economía y Competitividad, Spain). L. R.-A. agrradece a la Universidad de Granada su contrato puente (Plan Propio de Investigación, UGR)

Self-assembly in magnetic supramolecular hydrogels

Most recent advances in the synthesis of supramolecular hydrogels based on low molecular weight gelators (LMWGs) have focused on the development of novel hybrid hydrogels, combining LMWGs and different additives. The dynamic nature of the noncovalent interactions of supramolecular hydrogels, together with the specific properties of the additives included in the formulation, allow these novel hybrid hydrogels to present interesting features, such as stimuli-responsiveness, gel-sol reversibility, self-healing and thixotropy, which make them very appealing for multiple biomedical and biotechnological applications. In particular, the inclusion of magnetic nanoparticles in the hydrogel matrix results in magnetic hydrogels, a particular type of stimuli-responsive materials that respond to applied magnetic fields. This review focuses on the recent advances in the development of magnetic supramolecular hydrogels, with special emphasis in the role of the magnetic nanoparticles in the self-assembly process, as well as in the exciting applications of these materials

The microbiome of the uropygial secretion in hoopoes is shaped along the nesting phase

Microbial symbiont acquisition by hosts may determine the effectiveness of the mutualistic relationships. A mix of vertical and horizontal transmission may be advantageous for hosts by allowing plastic changes of microbial communities depending on environmental conditions. Plasticity is well known for gut microbiota but is poorly understood for other symbionts of wild animals. We here explore the importance of environmental conditions experienced by nestling hoopoes (Upupa epops) during the late nesting phase determining microbiota in their uropygial gland. In cross-fostering experiments of 8 days old nestlings, “sibling-sibling” and “mother-offspring” comparisons were used to explore whether the bacterial community naturally established in the uropygial gland of nestlings could change depending on experimental environmental conditions (i.e., new nest environment). We found that the final microbiome of nestlings was mainly explained by nest of origin. Moreover, cross-fostered nestlings were more similar to their siblings and mothers than to their stepsiblings and stepmothers. We also detected a significant effect of nest of rearing, suggesting that nestling hoopoes acquire most bacterial symbionts during the first days of life but that the microbiome is dynamic and can be modified along the nestling period depending on environmental conditions. Estimated effects of nest of rearing, but also most of those of nest of origin are associated to environmental characteristics of nests, which are extended phenotypes of parents. Thus, natural selection may favor the acquisition of appropriated microbial symbionts for particular environmental conditions found in nests.Support by funding was provided by Spanish Ministerio de Economía y Competitividad, European funds (FEDER) (CGL2013-48193-C3-1-P, CGL2013-48193-C3-2-P), and Junta de Andalucía (P09-RNM-4557). AM-G had a predoctoral grant from the Junta de Andalucía (P09-RNM-4557).Peer reviewe

Magnetorheological effect in the magnetic field oriented along the vorticity

Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The following article appeared in Kuzhir, P.; et al. Magnetorheological effect in the magnetic field oriented along the vorticity. Journal of Rheology, 58: 1829 (2014) and may be found at http://dx.doi.org/10.1122/1.4893586.In this work, we have studied the magnetorheological (MR) fluid rheology in the magnetic field parallel to the fluid vorticity. Experimentally, the MR fluid flow was realized in the Couette coaxial cylinder geometry with the magnetic field parallel to the symmetry axis. The rheological measurements were compared to those obtained in the cone-plate geometry with the magnetic field perpendicular to the lower rheometer plate. Experiments revealed a quasi-Bingham behavior in both geometries with the stress level being just a few dozens of percent smaller in the Couette cylindrical geometry at the same internal magnetic field. The unexpectedly high MR response in the magnetic field parallel to the fluid vorticity is explained by stochastic fluctuations of positions and orientations of the particle aggregates. These fluctuations are induced by magnetic interactions between them. Once misaligned from the vorticity direction, the aggregates generate a high stress independent of the shear rate, and thus assimilated to the suspension apparent (dynamic) yieldstress. Quantitatively, the fluctuations of the aggregate orientation are modeled as a rotary diffusion process with a diffusion constant proportional to the mean square interaction torque. The model gives a satisfactory agreement with the experimental field dependency of the apparent yield stress and confirms the nearly quadratic concentration dependency rY / U2:2, revealed in experiments. The practical interest of this study lies in the development of MR smart devices with the magnetic field nonperpendicular to the channel walls.This work has been supported by Projects P09-FQM-4787 (Junta de Andalucıa, Spain), “Factories of the Future” (Grant No. 260073, DynExpert FP7) and PICS 161801 project: “Magnetic nanocomposites for mechanical and biological applications” with Ural Federal University, Russia. In addition, L.R.-A. acknowledges financial support by Secretarıa de Estado de Educacion, Formacion Profesional y Universidades (MECD, Spain) through its FPU and Estancias Breves programs